1. Field of Invention
This invention relates generally to noise reduction, and more specifically to reduction of power spectral density levels of a broadband data signal using data encoding techniques.
2. Art Background
A data processing system transmits digital data words over a data transmission bus. Such a technique is widely employed in data processing systems used for a variety of purposes. Examples include personal computers, electronic cash registers, etc. To facilitate networking, which includes connecting together computers and input/output devices such as printers, scanners, etc., wireless networks may be used. The receivers for these wireless networks may be located within the same enclosure as the data devices and due to their proximity, are vulnerable to interference. A device that is part of a wireless network has a receiver and/or a transceiver to enable one-way or two-way communication with other devices on the wireless network. An example of a wireless network is the Bluetooth™ wireless network.
Transmission of data across the data transmission bus of the data processing system, often referred to in the art as a system bus, produces a broadband frequency spectrum when the time series signal representing the data word is transformed to the frequency domain. Thus, the broadband character of the data words is manifest as a background radio frequency (RF) noise level to the wireless network receiver. The magnitude of this RF noise level can be greater than the wireless network receiver's receiver noise level in the operational band of interest to the wireless network. Such a condition is undesirable, thereby reducing the wireless receiver's effective signal-to-noise ratio. A reduction in the wireless receiver's signal-to-noise ratio will limit the maximum distance that devices can be separated before the wireless network ceases to function properly.
Presently, the problem of radiated RF energy from the transmission of data along the system bus is addressed by electromagnetic shielding. This is possible since the data rate is low and the spectral noise density at the wireless receiver is not sufficient to interfere with the receiver. Electromagnetic shielding requires special material and adds cost to the data processing system. Electromagnetic shielding also requires engineering design and analysis, and is another element which increases the cost of current systems. Electromagnetic shielding is never perfect, and in some instances, particularly where the data rate is comparable to the frequency of the wireless network, will not provide adequate isolation of the wireless receiver's antenna or other components from the unwanted source of radiated RF energy, thereby degrading the performance of the wireless network.